In the slightly more than a century of having telephone service available in the United States, the public switched telephone system has constantly evolved and grown in complexity, size, and capabilities. From the days in which calls were routed by a human operator working a plug board to switch and complete calls, the capacity of the system in both volume of traffic and service options has expanded greatly. A telephone company central office or central office switch is a device to which multiple subscriber lines are connected, each of which is terminated by a telephonic device of a customer. For conventional residential telephone service, one or more telephone sets will be connected to the subscriber line. Additionally, the central office has multiple trunk circuits connecting it to other central offices. Other trunk circuits are provided to customers, such as trunks feeding a private branch exchange (PBX) switch in a business office.
Some early developments of enhanced telephone service include the introduction in the early 1960s of direct long distance dialing. Prior to that time, all long distance toll calls had to be handled by one or more human operators who set up the call circuit and activated billing equipment. An important feature of the enabling technology for direct long distance dialing is the capability of switches to collect, store, and forward data identifying the dialed digits, i.e., the called number. These were transmitted through the network, as the call was set up via a well known signaling scheme known as multifrequency (MF) signaling. MF signaling is a species of in-band signaling in that the information signals (identification of the called number) was transmitted by signals within the voice frequency band, over the same trunk circuits that carried the voice signal once the call was completed. This technology allowed a much higher volume of long distance traffic to be handled and helped to significantly improve telephone service and to meet the demand for more and more service in the United States during the 1960s and 1970s. The major drawback of in-band signaling techniques was that they occupied voice trunk capacity during call set up. Furthermore, if the call could not be completed for some reason, such as the called number across the country was busy, cross country trunk capacity was occupied while the call set up migrated its way through the network and the report of the busy was returned back over the voice lines to the calling party. Five to ten seconds, for thousands and thousands of busy calls per day, translates to significant usage of trunk capacity.
In the late 1970s and early 1980s, American Telephone & Telegraph Company (AT&T) developed early species of common channel interoffice signaling (CCIS). CCIS is essentially a network architecture for a switched telephone network in which information about a telephone call is transmitted over high speed data links that are separate from the voice circuits that are used to transmit the signals of the call itself. Early in the development of common channel interoffice signaling, it was recognized that the interoffice data signaling links could be designed to provide high speed digital data that could first determine whether a call could be completed prior to assigning trunk capacity to set up the voice link. Thus, with common channel interoffice signaling, if a caller in Atlanta is dialing a number is Seattle, the identity of the called number can be transmitted over the interoffice signaling data links from the originating central office in Atlanta to the terminating central office in Seattle. The terminating central office is the central office that services the called number. If the called number is busy, data providing this information is transmitted back over the interoffice signaling link to the originating central office in Atlanta that locally provides a audible busy signal to the caller. Therefore, no long distance trunk capacity is occupied during this process and the voice circuits between Atlanta and Seattle that formerly would have been used to attempt to complete the call remain free for other uses. If the called number in Seattle is not busy, various devices in the network respond to the information about this call to assign interoffice trunks to set up a connection for the call, and it is then completed.
The public switched telephone network has evolved in the 1980s to a complex and very versatile system, most of which supports and is controlled by a form of common channel interoffice signaling. The basics of this network were designed by AT&T. Development of the network by the Regional Bell Operating Companies (RBOC) as well as other independent local telephone service providers has continued since the judicially mandated divestiture of local exchange carriers by AT&T in 1984. The basic architecture of the switched telephone network is, in significant parts, identical throughout the United States and the developed industrialized world including western Europe and Japan. The specifics of the current network described in this specification are those employed by the RBOCs and other local exchange carriers operating in the United States. This network architecture is used by all modern telephone switching systems in the United States and is virtually identical to modern systems in western Europe and Japan. It is commonly referred to as the Advanced Intelligent Network (AIN). The need for the present invention results from an event that many people familiar with the telephone business in the United States believe will be forthcoming in the near future: provision of access to the Advanced Intelligent Networks operated by local exchange carriers to third parties so that they may provide competitive telephone related services to local exchange carrier subscribers. In other words, it is believed likely that either voluntarily or by regulatory mandate, the local exchange carriers (LECs) (i.e., the local telephone service providers) will be required to allow others to access the Advanced Intelligent Network that controls many modern features and services offered by telephone companies, including the setting up and taking down of voice connections.
In the modern intelligent public switched telephone network, the same signaling path described above that is used for basic call set up, take down and routing, is also used to provide enhanced custom calling features and to control the operation of billing equipment and maintain billing records. Thus, it will be appreciated that allowing access to this network to parties other than the local exchange carrier is a proposition that is fraught with peril. The careless or malicious party with access to the digital network that controls the telephone system and access to information stored therein can seriously hamper proper operation of the public switched telephone network, corrupt data stored therein, including billing data, or surreptitiously obtain private information stored within the network unless adequate precautions are taken if and when access to third parties is provided. Therefore, the present invention has been developed in anticipation of open access to the intelligent network of the public switched telephone system.
In order to understand both the need for the present invention and its implementation, it is first necessary to understand the fundamental architecture of the modern Advanced Intelligent Network and the points at which an interface may be provided to third parties. FIG. 1 of this specification is a block diagram representing at least part of the AIN of a typical local exchange carrier. While the diagram is simple, the components thereon are well known to those skilled in the art. A plurality of central office switches is provided in a typical public switched telephone network. These are indicated as SSP switches 15--15' in FIG. 1. The dashed line between these indicate that the number is arbitrary. Also, non-SSP switches, such as switch 16 are also included within the network. SSP is an acronym for Service Switching Point.
The difference between an SSP central office switch and a non-SSP central office switch is that the former includes intelligent network functionality. This is an indication that the switch is equipped with appropriate hardware and software so that, when a set of predetermined conditions are detected, the switch will initiate a trigger for a predetermined state of a call on a subscriber line, generate the trigger as an appropriate message to be sent out over the AIN, suspend handling of a call until it receives a reply from the network instructing it to take certain action. In the alternative, the switch will have a default task to execute if a timeout occurs and no response is provided by the network to the query made by the switch. In summary, the SSP switches are those that are fully equipped to deal with and take advantage of the Advanced Intelligent Network described herein.
Non-SSP switch 16 is an electronic switch that can generate certain rudimentary packets and provide them over the network, but which must rely on other equipment, described in greater detail hereinbelow, to provide subscriber lines connected to such a switch with more complex features and services available in the intelligent network. Central offices 15--15' and 16 each have a plurality of subscriber lines commonly designated as 17--17', connected thereto. Typically, the number of subscriber lines will be on the order of 10,000 to 70,000 lines. Each of subscriber lines 17--17' is connected to a terminating piece of customer premises equipment, that is represented by a like plurality of telephone sets 18--18' for each of the switches.
Interconnecting central office switches 15 and 16 are a plurality of trunk circuits indicated as 19a and 19b in FIG. 1. These are the voice path trunks that interconnect the central office and over which calls are connected when completed. It should be lo understood that central office trunking in a typical urban environment is not limited to a daisy chain arrangement implied by FIG. 1. In other words, in a typical network, trunk circuits will exist between central office switch 15' and central office switch 16. Therefore, when a local call is made between two central offices, if a direct trunk connection exists between the offices, and is not busy, the network will assign that trunk to the completion of that particular call. If there is no direct trunking between the two central offices, or the direct trunks are all in use, the call will be routed along trunks from the originating central office to at least one other central office, and through subsequent trunk connections on to the terminating central office.
This general architecture is magnified when a wider geographic area that includes multiple local exchange carriers is considered. In that case, the only significant difference is that certain inter exchange carrier switches that switch nothing but long distance trunk circuits are included.
Most of the intelligence of the intelligent switched telephone network resides in the remaining components shown on FIG. 1. These are the computers and switches that embody the current version of the common channel interoffice signaling scheme mentioned above. Each of switches 15 through 16 is connected to a local signal transfer point (STP) 20 via respective data links 21a, 21b, and 21c. Currently, these data links are 56 kilobit per second bidirectional data links employing a signaling protocol referred to as Signaling System 7 (SS7). The SS7 protocol is well known to those skilled in the art and is described in a specification promulgated by the American National Standards Institute (ANSI). The SS7 protocol is a layered protocol wherein each layer provides services for layers above it and relies on the layers below to provide it with services. The protocol employs packets that include the usual beginning and terminating flags and a check bit. Additionally, a signal information field is provided that includes a variable length user specific data and a routing label. A service information octet is provided that identifies a priority of the message, the national network of the destination of the message, and the user name identifying the entity that created the message. Also, certain control and sequence numbers are included within the packet, the uses and designations of which are known to those skilled in the art and described in the above referenced ANSI specification.
All of the SS7 data packets from the switches go to a signal transfer point (STP) 20. Those skilled in the art will recognize that signal transfer point 20 is simply a multi-port high speed packet switch that is programmed to respond to the routing information in the appropriate layer of the SS7 protocol, and route the packet to its intended destination. The signal transfer point is not normally, per se, the destination of a packet, but merely directs traffic among the other entities on the network that generate and respond to the data packets. It should be noted that signal transfer point devices such as STP 20 are conventionally installed in redundant pairs within the network so that if one device fails, its mate takes over until the first STP is able to return to service. In practice, there are redundant data links between each of central office switches 15 through 16 for enhanced reliability. For the sake of simplicity of the drawings, the redundant devices have not been illustrated in the drawing figures in this specification.
Also connected to signal transfer point 20 over SS7 data link 25 is a 1AESS network access point (NAP) 22. Network access point 22 is a computing device programmed to detect trigger conditions. It requires the support of an SSP switch to notify AIN network systems of these trigger detection events. An SSP can support multiple NAP switches. Logically, this SSP is designated as the destination address for many of the packets generated by the network that would otherwise be routed to the 1AESS NAP if it were an SSP equipped switch.
Much of the intelligence, and the basis for many of the new enhanced features of the network reside in the local service control point (SCP) 26 that is connected to signal transfer point 20 via SS7 data link 27. As is known to those skilled in the art, service control points are physically implemented by relatively powerful fault tolerant computers. Typical implementation devices include the Star Server FT Model 3200 or the Star Server FT Model 3300, both sold by American Telephone & Telegraph Company. The architectures of these computers are based on Tandem Integrity S2 and Integrity S1 platforms, respectively. In most implementations of a public switched telephone network, service control points are also provided in redundant mated pairs in order to assure reliability and continued operation of the network.
The computing devices implementing service control points typically accommodate one to twenty seven disk drives ranging from 300 megabytes to 1.2 gigabytes per drive, and have main memory on the order of 24 to 192 megabytes. Thus, it will be appreciated that these are large and powerful computing machines. Among the functions performed by the service control points are maintenance of network data bases used in providing enhanced services. The computers embodying the SCPs can execute at a speed on the order of 17 million instructions per second. Using the SS7 protocol, this translates to about 50 to 100 transactions (query/response pairs) of network messages per second.
Service control point computers were initially introduced into the network to handle the necessary translations and billing transactions for the implementation of 800 number service, i.e., toll free (to the caller) long distance service. An 800 number subscriber has at least one dial-up line number that is to be called when a call to that subscriber's 800 number is placed. There is no physical central office or area of the country that corresponds to the 800 area code. It is significantly more economical to provide a few central locations at which the lookup of the directory number for an 800 call can be made than to provide the translation information redundantly at many central office switches. Currently, service control points also include data bases for credit card call transactions.
Also, service control points include data bases that identify particular service customers. In order to keep the processing of data and calls as simple and generic as possible at switches, such as switches 15--15', a relatively small set of triggers are defined at the switches for each call. A trigger in the network is an event associated with a particular subscriber line that generates a packet to be sent to a service control point. The trigger causes the service control point to query its data base to determine whether some customized calling feature or enhanced service should be implemented for this particular call, or whether conventional plain dial-up telephone service should be provide for the call. The results of the data base inquiry are sent back to the switch from SCP 26 through STP 20. The return packet includes instructions to the switch as to how to process the call. The instruction may be to take some special action as a result of a customized calling service or enhanced feature, or may simply be an indication that there is no entry in its data base that indicates that anything other than plain telephone service should be provided for the particular call. In response to receiving the latter type message, the switch will move through its call states, collect the called digits, and generate further packets that will be used to set up and route the call, as described hereinabove.
Similar devices for routing calls among various local exchange carriers are provided by regional signal transfer point 28 and regional service control point 29. The regional STP 28 is connected to local STP 20 via an SS7 data link 30. The regional STP 28 is connected to the regional SCP 29 via a data link 31 that is physically and functionally the same as data link 27 between the corresponding local devices. As is the case with the local devices, regional STPs and STCs are provided in mated redundant pairs for the purposes of reliability.
Both local and regional service control points 26 and 29 are connected via respective data links 35 and 36 to a service management system (SMS) 37. The service management system is also implemented by a large general purpose digital computer and interfaces to business offices of the local exchange carrier and interexchange carriers. The service management system downloads information to the data bases of the service control points 26 and 29 when subscribers modify their ensemble of AIN services. Similarly, the service management system downloads, on a non-realtime basis, billing information that is needed in order to appropriately invoice telephone company subscribers for the services provided.
The modern Advanced Intelligent Network also includes service nodes (SNs) such as service node 39 shown in FIG. 1. Those skilled in the art will be familiar with service nodes, which are physically implemented by the same types of computers that embody the service control points 26 and 29. In addition to the computing capability and data base maintenance features, service node 39 also includes voice and DTMF signal recognition devices and voice synthesis devices. Service node 39 is connected to service management system 37 via a data link 40 that services the service node in essentially the same way it services SCPs 26 and 29. While service node 39 is physically quite similar to SCP 26, there are some important differences in the uses to which it is put. Service control points such as SCP 26 normally implement high volume routing services, such as call forwarding and 800 number translation and routing. They are also used for maintenance of and providing access to high volume data bases for authorization of billing, such as credit card number validations. In most local exchange carrier networks, service control points are only used for data base look up and routing services that take place prior to the logical completion of the call, i.e., the provision of a ringing signal to the called subscriber line and ring back to the calling subscriber.
By contrast, service nodes, such as service node 39, are used principally when some enhanced feature or service is needed that requires an audio connection to the call or transfer of a significant amount of data to a subscriber over a switched connection during or following a call. As shown in FIG. 1, service node 39 is typically connected to one or more (but normally only a few) switches via Integrated Service Digital Network (ISDN) links shown as 41. Thus, services that are implemented during a call (i.e., after completion of ringing or called subscriber pick up) usually employ the facility of a service node such as service node 39.
To give the reader an example, voice announcement of a calling party is a custom feature that is implemented via service node 39. Assume a subscriber dials the number of another subscriber, Ms. Jones, who subscribes to a service to provide voice announcement of incoming calls. One of the call progress states for an SSP equipped switch occurs after collection of the dialed digits when a termination request trigger is generated by the switch. This trigger consists of an SS7 data packet that is routed through STP 20 to SCP 26 and identifies the particular called party number. The SCP looks up the record for the directory number associated with Ms. Jones' phone line and detects that she is a subscriber to a service that provides voice announcements identifying incoming calls. SCP 26 then sends packets back over data link 27 to STP 20 that are routed to both the central office associated with the calling party's subscriber line and that of Ms. Jones.
The central office of the calling party is instructed to wait or place ring back on the calling party's subscriber line. Another packet is routed to switch 15'. It includes the identity of Ms. Jones' directory number, the calling party number, and a request for access to a voice synthesizer channel in service node 37. Switch 15' establishes a voice and data circuit over ISDN links 41 with the service node and passes a packet (in an appropriate ISDN format) to the service node. The service node then queries its data base to determine if there is an entry in Ms. Jones' record (actually the record for her directory number) for the particular calling number.
In the meantime, the necessary voice trunks have been connected between central office 15' and the central office serving Ms. Jones' telephone line and thus, a voice path exists between the synthesizer in service node 39 and Ms. Jones when answer supervision is returned on her subscriber line. The synthesizer will then announce the identity of the calling party and the person answering Ms. Jones' telephone can take appropriate action (such as pressing a particular number on the phone) to indicate whether or not they want to receive the call. The DTMF number is recognized by a DTMF recognition circuit in the service node that is likewise bridged onto the voice circuit. The service node then generates appropriate packets indicating whether the call has been accepted or rejected that travel over the ISDN link 41 to switch 15'. In the switch, protocol translation takes place so that the information in these packets is formatted into proper SS7 protocol packets that are then passed on to signal transfer point 20 and routed to appropriate offices to either set up the voice link between the calling party and Ms. Jones' subscriber line, or to provide appropriate audible indication (such as busy or reorder tone) to the calling party.
The foregoing description is a basic overview, together with a few examples, of the operation of the Advanced Intelligent Network that is a modern public switched telephone system. As will be apparent to both those skilled in the art and the casual but interested reader of this specification, the integrity of the data packets passing through the network is crucial to its operation. The integrity of the packets must be maintained in order for the system to function properly so that calls may be completed. Furthermore, since the SS7 data packets control the allocation of voice circuit capacity, it is critical to proper operation of the network that spurious or unneeded requests for trunk capacity not be generated within the network.
One result of the power and versatility of the modern intelligent switched telephone network is the possibility that inconsistent or problematic conflicting requests can be generated. One common example that needs to be avoided is known as a trigger loop. In its simplest form, consider the situation in which two subscribers of an AIN call forwarding custom calling feature each decided to go visit the other. In accordance with the rules of call forwarding, they pick up their phone and dial the appropriate digits to indicate the telephone number associated with their destination. This information is stored at service control point 26 for each subscriber.
If someone calls one of these subscribers, a termination request trigger for one of the telephone lines is generated. The SCP 26 looks in its data base and reports that this call should be forwarded to the other telephone number under consideration. This generates a packet that allocates a trunk circuit between the two telephones in order to complete the call to the forwarded destination. After this happens, the network generates a termination request trigger for the number to which the first subscriber's call has been forwarded. This trigger is acted upon by the SCP by noting that calls to that phone have been forwarded to the other friend's phone. In response to this, if nothing else is done, the network will allocate a second trunk circuit back from the second friend's phone to the first friend's phone, and likewise generate a termination request trigger identical to the original one. The process would continuously repeat itself.
If left unchecked, such a trigger loop would, very quickly (in view of the speed of the computers involved) allocate all of the existing trunk capacity available between these two friend's subscriber lines to a call that will never be completed. This would shut out all of the calls between these offices and furthermore occupy much alternate routing trunk capacity. Since these types of services are currently only under the control of the local exchange carriers, they will program their service control points to recognize a condition of a trigger loop and to terminate its operation in a graceful way so that trunk capacity is not tied up in a wasteful manner. Other solutions are possible for this specific problem, but there are many related scenarios, such as intra-switch trigger loops, or other more complex cases, which must be considered.
It should be quickly appreciated that the ability to quickly detect this type of trigger loop resides in the fact that the service control point computing device has access to all information about call forwarding orders in its data base, or in a data base that it can access over the network. The prospect of allowing private third party entities access to the SS7 signaling network that can reroute calls in a manner so that its destination is not reflected in the data bases maintained by the local exchange carrier leads to the possibility of undetected trigger loops when third parties are allowed to generate network orders for routing calls to subscriber lines other than the line associated with the directory number dialed at the call's origination. Furthermore, the ability to reroute calls via third party access to the network on its face leads to the possibility that the mischievous or unscrupulous operator could generate routing orders that would misdirect calls intended for one business to those of a competitive business.
The inventor of the present invention believes that opening the network SS7 data links to third parties so that they may provide customized services over the telephone network will be regulated so that the third party providers will not be required to provide extensive information to the local exchange carrier about the nature of the service provided. Thus, the prospect of opening the network to third party suppliers of enhanced calling services is one that requires careful mediation at the interface between the local exchange carrier network and the third party, and monitoring of activity and data packet messages to protect both the integrity and operation of the network and the privacy of all service providers' subscribers.
Furthermore, it is believed that there will be no prohibition against individual telephone subscribers ordering different forms of enhanced services from separate third party vendors. Under these circumstances, the local exchange carrier might have no information about various services, and even the third party suppliers might not know that a particular subscriber is a customer of another entity for another service. Under these circumstances, the order in which triggers are passed across an interface to a third party provider of services can affect the net result of the services to the subscriber. For example, if a particular subscriber was a call forwarding customer of one service and a call screening customer of another service, the order in which the triggers were reported to the respective providers of these services will affect whether all of the subscriber's calls are screened. A call screening service is one that will block incoming calls originated from certain subscriber lines. It is a service that provides the possibility of reestablishing some of the privacy that the ubiquitous use of telephones has eroded in the modern world.
If the termination request trigger for the particular called subscriber is first provided to the entity providing the screening service, then all calls to the subscriber will be properly screened. If, however, the trigger is first provided to the entity providing the forwarded service, and the subscriber has indeed forwarded his or her calls, the next termination request trigger that is generated will be for the number to which the line has been forwarded. This will not be detected as a trigger that requires service by the entity providing the screening process and thus, forwarded calls will not be screened. It is therefore believed by the inventor that a hierarchy or sequence of provision of triggers for various services may need to be specified by subscribers in addition to the technical constraints that require avoidance of undesirable feature interactions.
It is anticipated that third party enhanced service providers who are given access to the intelligent network will be billed for use of the network capacity based on the number of query/response pairs they generate within the network. This is believed by the inventor to be the most likely scenario for a tariff for this service since it is relatively easy to maintain a count that is a measure of the use of local exchange carrier equipment that is made by the outside service provider. So long as the Advanced Intelligent Network remains closed, local exchange carrier designers could predict network traffic and thus, make plans for expansion of the capacity of the network with a relatively high degree of confidence. The opening of the network to third party providers will require some estimation from the third party service providers as to the number of query/response pairs (i.e., packets or network messages) that provision of their service will produce so the local exchange carriers can estimate the impact of the outside service on the network.
The impact can be manifested in two basic ways. The first is a consideration of total packet traffic generated by the outside service provider over a relatively long period of time, such as a day. The second aspect that must be considered is the time rate of generation of packets by the third party service provider. Outside service providers may provide services that have a relatively low average number of messages per unit time over each day, but may generate a very high volume of traffic in a small window of time. Numerous occurrences of high density traffic bursts from several non-local exchange carrier (non-LEC) entities can impede the working of the rest of the telephone network, including the slowing down of the delivery of dial tone, or the occupation of an undue amount of trunk capacity. With LEC provided services, the local exchange carrier can customize responses to high message content services, such as provision of radio contest call-in lines. However, it is anticipated that local exchange carriers will have very little information about the nature of the services provided by third parties if the network is opened and thus, there is a need for mediating traffic and protecting the network in real time at the interface provided to the third party supplier. There is a need for the network to be able to respond by disabling a problem source that is generating message traffic at too high a density, or is failing to respond appropriately to triggers and other messages routed to it and therefore, causing a large number of devices, particularly at SSP switches, to wait for a timeout before proceeding with call handling.
Also, much of the information maintained in data bases within the :network can constitute sensitive business information of the customers of the local exchange carriers. Information on the rate at which a business receives telephone calls, the 800 number traffic it experiences, or even the temporal characteristics of calls to particular businesses can constitute information that might be useful to a business competitor of an LEC customer. Therefore, if the network is opened, there is a need to carefully check and restrict the type of information to which non-LEC customers are given access.
The current use of separate SS7 signal packets to control call routing was, in significant part, motivated by a need to reroute calls in order to provide custom calling services or enhanced services. The simplest example is, of course, the forwarding of a call intended for one subscriber line to another one. However, the ability to reroute calls to a subscriber line other than that associated with the number dialed also leads to a potential for business mischief if and when the network is opened to third party generators of data packets.
For example, if not controlled, a competitor of one business that uses inbound phone calls as a significant source of new customers could generate a packet on the network that instructed a service control point computer to forward a call from a competitor to the phone of the business entity that generated the network message. This could be done periodically, leaving the forwarding order in place for only short periods of time, so that a certain percentage of incoming calls were bled off in this fashion. Thus, in the event the network is opened to third parties, there is a need to protect the integrity of the call routing process from unauthorized or improper attempts to reroute calls or interfere with calls that the third party entity having access to the network should not affect.
In summary, the Advanced Intelligent Network is a complex high speed, high traffic volume packet switched messaging arrangement that provides a great deal of versatility in the handling of telephone calls. Most network elements, and in particular the SSP switches, are designed so that a relatively simple format of a query message is generated upon certain events and the switch will wait for a response from the network before proceeding with call processing. These procedures employ a watchdog timer that will timeout in the event a response to the query is not received. However, in circumstances where further call progress was controlled by the occurrence of timeouts, as opposed to a valid response, for a large percentage of the calls being processed, there would be a significant deterioration in the performance of the network. It would cause customers to experience undue delays in call processing or the inability to have enhanced features properly provided. Fundamentally, it is the versatility of the network that leads to its vulnerability to inappropriate network messages. Therefore, if and when the network is opened so that access to the Advanced Intelligent Network is available to third party enhanced service providers, there is a need to provide mediation of message traffic across the interface between the local exchange carrier and the third party service provider, and to protect the network from mischief, human error, and equipment failure on the third party service provider's side of the interface.